1. Field of the Invention
The present invention relates to a surface roughening method for an organic electrophotographic photosensitive member. More particularly, it relates to a surface roughening method that forms the surface of an organic electrophotographic photosensitive member into a uniformly roughened surface in a short time.
2. Related Background Art
Electrophotographic photosensitive members, when used, are set into electrophotographic apparatus comprising at least the steps of electrostatic charging, imagewise exposure, development, transfer, and cleaning. In carrying out such an electrophotographic process, the step of cleaning to remove remaining toner after transfer is required in any developing processes.
Methods of carrying out this cleaning usually include the following two types. One of them is a method in which a rubber material called a blade is brought into pressure contact with a photosensitive member so that there may be no gap between the photosensitive member and blade and thus the toner can be prevented from slipping through the gap. The other of them is a method in which the roller of a fur brush is rotated in such a manner that the brush may come into contact with the surface of a photosensitive member to wipe off or brush off the toner. Of these, the latter method tends to allow the toner to slip through, unless the brush is brought into firm contact with the photosensitive member, or may scratch the photosensitive member if the toner having collected on the fur brush is fused. Moreover, the rubber blade is more inexpensive and can be designed with greater ease. For these reasons, cleaning using the blade is prevails at present. In particular, in carrying out the natural color developing that has been put into practical use in recent years, the toner is used in a much larger quantity than the ordinary single-color developing since the natural color is produced by overlapping the three primary colors of magenta, cyan and yellow, or four colors in which black is further included. Thus, it is most suited to use the cleaning method in which the rubber blade is brought into pressure contact with the photosensitive member.
In instances in which the cleaning of a wet toner is carried out using this cleaning blade, the wet toner itself and a solvent therefor, which are comprised of fine particles, come into the gap between the cleaning blade and photosensitive member surface to play a role as a lubricant, so that there has been no problem.
In instances in which the cleaning of a dry magnetic toner is carried out using this cleaning blade, however, this toner itself has such a good ability for abrading the photosensitive member surface that the surface of the photosensitive member can be readily roughened and hence the lubricity or slipperiness between the photosensitive member surface and cleaning blade can be improved. However, at the initial stage in using the photosensitive member, there is a large frictional force between the photosensitive member surface and blade because of a lack of roughness on the photosensitive member surface at that stage, sufficient to the cause the cleaning blade to reverse direction. Thus the surface must be coated with a lubricant.
In the case when a dry non-magnetic toner must be used with the introduction of color systems, the toner used therefor has a photosensitive member surface-abrasive power of only not more than one-tenth of that of the magnetic toner. Although iron powder or ferrite, or these materials coated with resins, used as a magnetic material (carrier), can brush the photosensitive member when developing is carried out, this dry two-component developing system can achieve a photosensitive member surface-abrasive powder of only about one-third of that of the dry one-component developing system. For this reason, when the dry non-magnetic toner is used, the friction between the photosensitive member surface and blade can not be sufficiently relieved, tending to cause the problems of blade reversing, edge breaking, or the like.
When the natural color developing is used, the problems which are seriously caused are such that the cleaning blade reverses, and the blade edges are torn off and broken. This is because natural color developing, which employs the dry two-component developing system, results in a poor photosensitive member surface-abrasive powder as shown above and, in addition thereto, because of the following reasons (1) and (2):
(1) Since the developing is carried out three or four times corresponding to the three primary colors of magenta, cyan and yellow, or the four colors including black, to produce a sheet of image, the processing is required to be carried out at a higher speed, resulting in an increase in the friction applied to the cleaning blade.
(2) Since the three or four color toners transferred to paper must be fixed so that they may be sufficiently melted and mixed, it is necessary to use toners with a low glass transition point (Tg), i.e., a Tg of not more than 60.degree. C. that results in a toner having a high agglomeration and adhesion and weaken its function as a lubricant, which function is possessed by conventional toners that enter into the gap between the cleaning blade and photosensitive member surface to improve the lubricity.
The troubles of the cleaning blade reversing and edge breaking tend to more often occur when the photosensitive member surface is hard, i.e., made with little abrasiveness so that the photosensitive member can have a longer life time. Moreover, when the toner particle size is made uniform and fine toner is removed in order to improve image quality, the lubricity produced when the toner enters into the gap between the cleaning blade and photosensitive member surface is more diminished, tending all the more to cause the blade reversing or edge breaking.
In the instance in which a surface layer of the photosensitive member comprises an organic matter, the frictional resistance between the blade and photosensitive member surface may increase, particularly tending to cause blade turn-up or the like, when compared with a member having an inorganic surface.
To settle such problems, the present applicants have proposed to previously make the photosensitive member surface rough, as disclosed in Japanese Patent Laid-open No. 1-99060 corresponding to U.S. Ser. No. 253082 filed Oct. 4, 1988 now abandoned. This enables reduction of the contact area between the photosensitive member surface and cleaning blade, and also makes it possible to prevent the cleaning defects such as cleaning blade reversing, by virtue of the lubricity produced when the fine toner appropriately creeps into the gap between the photosensitive member surface and blade.
On the other hand, as a method of roughening the surface of a photosensitive member, a method is known in which powder particles are previously included in a surface layer of a photosensitive member by coating, to provide a roughened surface, as disclosed in Japanese Patent Laid-open No. 52-26226. In this method, however, it has been difficult to control the degree of surface roughness, and a uniform roughened surface has been obtainable with difficulty. Another method is known in which the resilience at tips of a metallic wire or fiber brush is utilized to abrade the surface of a photosensitive member, as disclosed in Japanese Patent Laid-open No. 57-94772. In this method, however, it has been difficult to carry out uniform surface-roughening in a short time, and scratches on the photosensitive member surface may be produced, tending to cause defective images.